(a) Field of the Invention
The present invention relates to a method for improving the antiretroviral activity of a cytidine analogue reverse transcriptase inhibitor; a boosted cytidine analogue reverse transcriptase inhibitor antiretroviral compound; an antiretroviral oral formulation to inhibit viral replication in HIV infected patients comprising efficient amounts of two different cytidine analogue reverse transcriptase inhibitors of different dosages in a pharmaceutically acceptable carrier to produce boosted cytidine analogue reverse transcriptase inhibitor antiretroviral compound in a patient cell; a method for the therapy of HIV infected patients comprising orally administrating the oral formulation.
(b) Description of Prior Art
An estimated 38.6 million people worldwide were living with HIV in 2005 according to the World Health Organization (WHO) (UNAIDS/WHO, 2006 Report on the Global AIDS epidemic. UNAIDS-Geneva, Switzerland, 2006.). Approximately 4.1 million persons acquired the human immunodeficiency virus (HIV) and 2.8 million individuals died in 2005 (UNAIDS/WHO, 2006.).
According to WHO, new simplified and less expensive approaches suitable for resource-poor settings are of greatest need.
Since the introduction of combination antiretroviral therapy, especially with the introduction of highly active antiretroviral therapy (HAART), HIV-related morbidity and mortality diminished significantly. However, in spite of progress and huge efforts, the HIV epidemic continues to expend (UNAIDS/WHO, 2006.). Moreover, HAART also led to the emergence, at an increasing rate, of adverse effects, metabolic abnormalities, body changes as well as drug resistance.
In order to offset these problems, new drugs, new drug combinations or approaches are continuously evaluated.
Antiretroviral regimens usually contain 2 nucleoside analogue reverse transcriptase inhibitors (NRTI) plus a protease inhibitor (PI) or a non-nucleoside reverse transcriptase inhibitor (NNRTI). Examples of NRTI are AZT (azidothymidine, zidovudine), d4T (stavudine), 3TC (lamivudine), ddC (zalcitabine), ddI (didanosine), abacavir (ziagen), FTC (emtricitabine). The approved NNRTI are: nevirapine, delavirdine, efavirenz. Among the protease inhibitors are saquinavir, indinavir, ritonavir, nelfinavir, lopinavir, atazanavir, amprenavir and tipranavir.
One of the most extensively utilized antiretroviral drugs being the backbone of most regimens is 3TC (2′ deoxy-3′-thiacytidine or lamivudine). In addition to its excellent safety profile, this drug has beneficial virologic effects even in the presence of a mutation at the position 184 (M184V) of HIV reverse transcriptase conferring high-level resistance to 3TC (Diallo K, Götte M, and Wainberg M A. Molecular impact of the M184V mutation in human immunodeficiency virus type 1 reverse transcriptase. Antimicrob Agents Chemother 2003, 47: 3377-3383). This beneficial antiretroviral activity could be augmented by increasing the intracellular concentration of 3TC active form.
As for other NRTIs, 3TC requires intracellular metabolism to its active form 5′-triphosphate (3TC-TP) as seen in FIG. 2. This will compete with the natural endogenous nucleoside for the incorporation into nascent proviral DNA and will lead to DNA chain termination and consequently inhibition of HIV replication. The antiretroviral activity of 3TC (as that of the other NRTIs) is directly correlated with the intracellular 3TC-TP concentration. Both extracellular and intracellular factors affect this activation (phosphorylation to triphosphate). In vitro studies showed that, at an extracellular concentration of 10 μM of 3TC, there is clear evidence of saturation of 3TC-TP formation; in other words higher extracellular 3TC concentrations which may be obtained with higher 3TC doses do not necessarily increase the level of the active intracellular form, the 3TC-TP (Gray N M, Marr C L P, Penn C R, Cameron J M, and Bethell R C. The intracellular phosphorylation of (2′, 3′)-2-deoxy-3′-thiacytidine (3TC) and the incorporation of 3TC 5′-monophosphate into DNA by HIV-1 reverse transcriptase and human DNA polymerase γ. Biochem Pharmacol 1995, 50: 1043-1051). This fact was also confirmed in clinical studies in which an increased dose of 3TC (300 mg instead of 150 mg) did not significantly increased the 3TC-TP levels and did not result in a better clinical, virologic or immunologic effect (Eron J J, Benoit S L, Jemsek J, et al. Treatment with lamivudine, zidovudine, or both in HIV-positive patients with 200 to 500 CD4+ cells per cubic millimeter. N Engl J Med 1995, 333: 1661-1669.).
As the activation pathways for 3TC and of another NRTI, ddC (2′-3′-dideoxycytidine), are similar (as seen in FIG. 2 ), it is conceivable that concomitant administration of these drugs will influence each other's activation.
Initial in vitro data (with huge, non-physiologic doses of ddC) showed a negative interaction between 3TC and ddC (Veal G J, Hoggard P G, Barry M G, Khoo S, Back D J. Interaction between lamivudine (3TC) and other nucleoside analogues for intracellular phosphorylation. AIDS 1996, 10: 546-548). Therefore, the concurrent use of ddC (daily doses of 2.25 mg) and 3TC are currently contraindicated because of their reciprocal inhibition of activities (ddC competes with the 3TC's activation and vice versa).
In conclusion, so far, no valid approach to increase intracellular 3TC-TP and, hence, its antiretroviral activity, was reported. It is imperative and timely to find a new therapeutic approach able to increase intracellular levels of 3TC-TP without increasing the drug-related toxicities, especially in patients harboring an HIV strain with reduced 3TC susceptibility or with a suboptimal control of HIV infection.